Boundary filtering method for intra prediction

ABSTRACT

Disclosed is a boundary filtering method for intra prediction, relating to the video encoding technology filed. Whether boundary filtering is performed on an intra prediction block or not is adaptively selected by means of a rate distortion optimization decision; during filtering, a filter coefficient exponentially attenuated relative to distance to boundary is adopted to perform filtering on the first N rows or the first N columns of the intra prediction block by means of an intra prediction block filter, and different filtering strengths are used according to different sizes of the prediction blocks. Therefore, the boundary distortion problem of intra prediction block is solved, the intra prediction precision is improved, and the encoding efficiency of intra prediction block is increased; and the practicability and the robustness of the boundary filtering technology are improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. § 371 ofPCT/CN2018/107209, filed on Sep. 25, 2018 which claims priority to CNApplication No. 201711095964.9 filed on Nov. 9, 2017. The applicationsare incorporated herein by reference in their entirety.

FIELD

The present disclosure relates to the video encoding technology field,and more particularly relates to a boundary filtering method for intraprediction.

BACKGROUND

Intra filtering is a very effective coding tool, which is used tooptimize the boundary of the intra prediction block, and can effectivelyalleviate the distortion at the boundary of the intra prediction block.

In the high efficiency video coding (HEVC) standard, two kinds ofboundary filtering for intra prediction are used.

One is to use a two tap filter (filter coefficient is [1/43/4]) tofilter the first row and the first column of the intra prediction blockfor the DC (Direct Current) prediction mode; the other is to filter thefirst row of the horizontal prediction mode and the first column of thevertical prediction modes for the horizontal and vertical predictionmodes.

The main defects of the above filtering technology include the followingaspects:

(1) the above existing filtering technology is only for a few intraprediction modes, so the performance of the intra filtering technologyis limited to a certain extent;

(2) these filtering techniques do not consider the spatial correlationbetween pixels in detail;

(3) the use of these filtering techniques lacks decision-making process,which reduces the practicability of these filtering techniques.

SUMMARY

To overcome the drawbacks the prior art, the present provides a boundaryfiltering method for intra prediction, which can effectively solve theproblem of boundary distortion of intra prediction block, improve theintra prediction precision, and increase the coding efficiency of theintra prediction block.

The technical solution provided by the present invention is as follows:a boundary filtering method for intra prediction, whether boundaryfiltering is performed on an intra prediction block or not is adaptivelyselected by means of a rate distortion optimization (RDO) decision. Theboundary filtering method filters the first N rows or the first Ncolumns of the intra prediction block by means of an intra predictionblock filter. During filtering, a filter coefficient exponentiallyattenuated relative to distance to boundary is adopted to performfiltering; and different filtering strengths are used according todifferent sizes of the prediction blocks. The boundary filtering methodcan effectively solve the problem of boundary distortion of intraprediction block, improve the intra prediction precision, and increasethe coding efficiency of the intra prediction block, which comprising:

1) at the encoding side, performing rate distortion optimization on eachcoding unit; comprising:

11) performing intra prediction block filtering for each coding unit;

12) determining whether intra prediction block boundary filtering shouldbe used at the encoding side by means of a RDO decision; transmitting aflag to the bitstream to identify whether intra prediction blockboundary filtering is used for intra prediction;

13) when intra prediction block boundary filtering should be used at theencoding side, intra boundary filtering coding is performed by the intraprediction block filter, which including the following processes:

first, obtaining reference pixels adjacent to the current block from thereconstructed prediction blocks;

subsequently, intra prediction is performed according to the predictiondirection of the intra prediction block to obtain an intra predictionvalue;

finally, the reference pixels for boundary filtering are selectedaccording to the prediction mode of the current intra prediction block,and filter coefficients are selected according to the size of theprediction block; the current prediction value is subjected to boundaryfiltering using the reference pixels to obtain a new intra predictionvalue;

2) at the decoding side, reading the flag in the bitstream for eachcoding unit and decoding according to the flag, which including thefollowing processes:

21) determining whether intra prediction block boundary filtering shouldbe used at the decoding side;

22) when intra prediction block boundary should be used at the decodingside, intra boundary filtering decoding is performed by the intraprediction block filter, which including the following processes:

first, obtaining reference pixels adjacent to the current block from thereconstructed prediction blocks;

then, intra prediction is performed to obtain the intra prediction valueaccording to the prediction mode of the intra prediction block that isobtained by decoding;

finally, reference pixels for boundary filtering are selected accordingto the prediction mode of the current intra prediction block, and filtercoefficients are selected according to the size of the prediction block,and the current prediction value is filtered using the reference pixelsto obtain a new intra prediction value.

The core of the present disclosure is to filter the pixel value obtainedafter intra prediction, including processing the encoding end and thedecoding end.

Specifically, at the coding end, when performing rate distortionoptimization (RDO) for each coding unit (Cu), it is necessary to try toperform intra prediction block filtering, and decide whether to use theintra prediction block filtering method proposed by the present finallyby means of RDO. Each coding unit needs to transmit a flag with 1-bit tothe bitstream to identify whether the intra prediction uses the intraprediction block filtering method. At the decoding end, the flag with1-bit in the bitstream is read. According to the meaning of the flag,the decoding end decides whether to use intra prediction block filteringor not.

In this method, the first N rows or first N columns of the intraprediction block are filtered, wherein, the value of N is related to thefiltering coefficient. Because the filter coefficient exponentiallyattenuated relative to distance to boundary is adopted in the present, Nis the position when the filter coefficient attenuates to 0. Forexample, if the filter attenuates to 0 on line n, then the value of N isn. The intra prediction block filtering provided by the present canfilter at most the first 10 rows or the first 10 columns of the intraprediction block.

The intra prediction block filter provided by the present invention is athree-tap filter, which is expression as formula 1:P′(x,y)=w _(left)(x)·P(−1,y)+w _(top)(y)·P(x,−1)+(1−w _(left)(x)−w_(top)(y))·P(x,y)0≤x,y<N  (formula 1)for a prediction pixel, two reference pixels, pixel P(−1,y) in the samerow thereof and pixel P(x,−1) in the same column thereof, are used forfiltering, wherein, w_(left)(x) and w_(top)(y) are the boundaryfiltering coefficients of the two reference pixels respectively, P(x,y)is the predicted pixel after the intra prediction; P′(x,y) is the pixelafter the intra prediction block filtering; x, y are the coordinateswithin the prediction block, it is the first column in the predictionblock when x=0, it is the first row in the prediction block when y=0; nis the number of rows or columns. w_(left)(x) and w_(top)(y) attenuateas the distance from the reference pixel increases.

In particular, when w_(top)(y) attenuates to 0, the intra predictionblock filter degenerates into a two-tap filter, as shown in formula 2.When w_(left)(y) attenuates to 0, the intra prediction block filterdegenerates into a two-tap filter, as shown in formula 3.P′(x,y)=w _(left)(x)·P(−1,y)+(1−w _(left)(x))·P(x,y),x<N   (formula 2)P′(x,y)=w _(top)(y)·P(x,−1)+(1−w _(top)(y))·P(x,y),y<N   (formula 3)

The filter coefficient exponentially attenuated relative to distance toboundary is used for filtering in the intra prediction block filterprovided by the present invention, wherein the filter coefficients areexpressed in formula 4 and formula 5 respectively:

$\begin{matrix}{w_{top} = \frac{n_{top}}{2^{y}}} & \left( {{formula}\mspace{14mu} 4} \right) \\{w_{left} = \frac{n_{left}}{2^{x}}} & \left( {{formula}\mspace{14mu} 5} \right)\end{matrix}$Where, n_(top) and n_(left) are filter coefficients used for filteringwith the first row and the first column of the prediction block,respectively. The filter coefficient with exponential attenuation can pbetter filtering effect and minimize prediction distortion.

Different filtering strengths are used according to different sizes ofthe intra prediction blocks in the present invention, wherein the filterintensity parameters n_(top) and n_(left) are obtained according to theprediction distortion training of the intra prediction block.

For the intra prediction value with large prediction distortion, alarger filter coefficient is selected for filtering; for the intraprediction value with small prediction distortion, a smaller filtercoefficient is used for filtering. The setting of the filter coefficientis described in the specific embodiment.

Compared with the prior art, the advantages of the present invention areas follows:

The present provides a boundary filtering method for intra prediction,which can effectively solve the problem of boundary distortion of intraprediction block, improve the intra prediction precision, and increasethe coding efficiency of the intra prediction block.

In particular, the technical advantages of the present are embodied inthe following aspects:

The present determines whether to use intra prediction block boundaryfiltering with RDO decision, which is equivalent to adaptive selectionof whether to carry out boundary filtering on the intra predictionblock. Because not every prediction block is suitable for boundaryfiltering, the practicability and robustness of boundary filteringtechnology are increased with RDO decision.

Moreover, the boundary filter proposed in the invention can modify morerows or columns (up to 10 rows or columns, while in the prior art, itonly filters 4 rows or columns of the boundary at most), which greatlyenhances the influence range of the boundary filter and improves theeffectiveness of the intra prediction boundary filter.

In addition, the filter coefficient exponentially attenuated relative todistance to boundary is proposed, which is more consistent with thespatial correlation between pixel values. And according to differentintra prediction modes and prediction block sizes, different filtercoefficients can be selected to get better filtering effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the coding flow diagram of the coding unit (Cu) in theinvention;

FIG. 2 shows the decoding flow diagram of the coding unit (Cu) in theinvention;

FIG. 3 shows a schematic diagram of boundary filter reference pixelselection in the specific implementation of the invention;

FIG. 4 shows the distribution diagram of edge prediction distortion foreach prediction mode of 16×16 prediction block in HEVC;

In the diagram, abscissa represents different prediction modes; ordinaterepresents the magnitude of edge distortion of prediction block; theline connecting blocks represents the distortion of the first row at thetop of prediction block; the line connecting triangles represents thedistortion of the first column on the left of prediction block.

FIG. 5 shows the schematic diagram of the intra prediction boundaryfilter coefficient in HEVC.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be further described by embodiments incombination with the drawings, but the scope of the present inventionwill not be limited in any way.

The present invention provides an effective intra prediction filteringmethod, whether boundary filtering is performed on an intra predictionblock or not is adaptively selected by the decision of RDO; the intraprediction block filtering proposed by the present invention filters thefirst N rows or the first N columns of the intra prediction block, andthe value of N is related with the filtering coefficient. Because thefilter coefficient exponentially attenuated relative to distance toboundary is adopted in the present, N is the position when the filtercoefficient attenuates to 0. For example, if the filter attenuates to 0on line n, then the value of N is n. The intra prediction blockfiltering provided by the present can filter at most the first 10 rowsor the first 10 columns of the intra prediction block; coefficient withattenuated relative boundary distance exponent is adopted to performfiltering on; and different filtering strengths are used according todifferent sizes of the prediction blocks. The boundary filtering methodcan effectively solve the problem of boundary distortion of intraprediction block, improve the intra prediction precision, and increasethe coding efficiency of the intra prediction block.

FIG. 1 shows the coding flow diagram of the coding unit (Cu) in theinvention. For an intra coding unit, the conventional intra coding (thatis, the intra frame coding algorithm currently used by the existingencoder) is carried out firstly, and then the intra boundary filteringcoding (that is, the coding method including the intra prediction blockboundary filtering technology) proposed by the present invention isused, that is, after the conventional intra prediction, the boundary ofthe intra prediction block is filtered by the boundary filter. Then, RDO(rate distortion optimization) is used to choose whether to use intraprediction boundary filtering, and a flag with 1-bit is output to thebitstream.

FIG. 2 shows the decoding flow diagram of the coding unit (Cu) in theinvention. For an intra coding unit, the flag with 1-bit is readfirstly, and then the conventional intra prediction is performed. Thendetermining whether the decoding side uses intra prediction boundaryfiltering or not according to the value of the flag. If there is no needfor boundary filtering, the reconstruction of the intra prediction blockcan be done directly; otherwise, the reference pixels used for boundaryfiltering should be selected according to the prediction mode of thecurrent intra prediction block, and the filtering coefficient should beselected according to the size of the prediction block, and the currentprediction value should be filtered using the reference pixels to obtaina new intra prediction value. Then the intra prediction block isreconstructed.

In order to avoid floating-point calculation, the boundary filterproposed in the present invention can use the filtering method shown informula 6, 7 and 8.P′(x,y)=(w _(left)(x)·P(−1,y)+w _(top)(y)·P(x,−1)+(64−w _(left)(x)−w_(top)(y)·P(x,y)+32)>>6   (formula 6)P′(x,y)=(w _(left)(x)·P(−1,y)+(64−w _(left)(x))·P(x,y)+32)>>6   (formula7)P′(x,y)=(w _(top)(y)·P(x,−1)+(64−w _(top)(y))·P(x,y)+32)>>6   (formula8).

That is, the filter coefficients of floating point are converted tointegers and the right shift operation is carried out after filtering.

The intra prediction block filter of the present invention uses one ortwo reference pixels closest to the prediction pixels for filtering. Asshown in FIG. 3, the position pointed by the arrow is the referencepixel used for filtering the predicted pixels A, B and C. It is usingthe reference pixel corresponding to its left side for filtering thepixel A, it is using the reference pixel on its upper side forfiltering, and the pixel C is located in the upper and left corner areaof the prediction block, so the reference pixels on its upper side andleft side are used for filtering it at the same time.

The intra prediction block filter of the invention adopts a filtercoefficient exponentially attenuated relative to distance to boundary.The filter intensity parameters, n_(top) and n_(left), are obtainedaccording to the prediction distortion statistics of the intraprediction block. FIG. 4 illustrates a distribution diagram ofprediction distortion for 16×16 intra prediction block statistics inHEVC. The filtering intensity parameters n_(top) and n_(left) aredefined to be proportional to the magnitude of prediction distortion,which are expressed as formula 9 and 10:

$\begin{matrix}{n_{top} = {\min\left( {\frac{d_{top}}{16},1} \right)}} & \left( {{formula}\mspace{14mu} 9} \right) \\{n_{left} = {\min\left( {\frac{d_{left}}{16},1} \right)}} & \left( {{formula}\mspace{14mu} 10} \right)\end{matrix}$

Wherein, d_(top) is the average prediction distortion value of the firstrow at the top of the prediction block, and d_(left) is the averageprediction distortion value of the first column on the left of theprediction block, “min” means take the minimum value of two values. Itcan be seen that the maximum value of n_(top) or n_(left) is 1.

For the prediction mode of specific direction, the filter coefficientsneed to be changed. Taking tue intra prediction mode of HEVC in FIG. 5as an example, in modes 2-9, when filtering the columns on the left sideof the intra prediction block, the filtering coefficient is reduced tohalf of the original coefficient, and the value of w_(left) becomes halfof the value of w_(top); similarly, in modes 27-34, when filtering therows on the top of the intra prediction block, the filtering coefficientw_(top) is reduced to half of the original.

It should be noted that the purpose of the disclosure of the embodimentsis to help further understand the present invention, but those skilledin the art can understand that various substitutions and modificationsare possible without departing from the spirit and scope of theinvention and the appended claims. Therefore, the present inventionshall not be limited to the contents disclosed in the embodiments, andthe scope of the present invention to be protected shall be subject tothe scope defined in the claims.

We claim:
 1. A boundary filtering method for intra prediction, whetherboundary filtering is performed on an intra prediction block or not isadaptively selected by means of a rate distortion optimization decision;during filtering, a filter coefficient exponentially attenuated relativeto distance to boundary is adopted to perform filtering on the first Nrows or the first N columns of the intra prediction block by means of anintra prediction block filter, and different filtering strengths areused according to different sizes of the prediction blocks,comprising: 1) at the encoding side, performing rate distortionoptimization on each coding unit; comprising: 11) performing intraprediction block filtering for each coding unit; 12) determining whetherintra prediction block boundary filtering should be used at the encodingside by means of a rate distortion optimization decision; transmitting aflag to the bitstream to identify whether intra prediction blockboundary filtering is used for intra prediction; 13) when intraprediction block boundary filtering should be used at the encoding side,intra boundary filtering coding is performed by the intra predictionblock filter, which including the following processes: first, obtainingreference pixels adjacent to the current block from the reconstructedprediction blocks; subsequently, intra prediction is performed accordingto the prediction direction of the intra prediction block to obtain anintra prediction value; finally, reference pixels for boundary filteringare selected according to the prediction mode of the current intraprediction block, and filter coefficients are selected according to thesize of the prediction block; the current prediction value is subjectedto boundary filtering using the reference pixels to obtain a new intraprediction value; 2) at the decoding side, reading the flag in thebitstream for each coding unit and decoding according to the flag, whichincluding the following processes: 21) determining whether intraprediction block boundary filtering should be used at the decoding side;22) when intra prediction block boundary should be used at the decodingside, intra boundary filtering decoding is performed by the intraprediction block filter, which including the following processes: first,obtaining reference pixels adjacent to the current block from thereconstructed prediction blocks; then, intra prediction is performed toobtain the intra prediction value according to the prediction mode ofthe intra prediction block that is obtained by decoding; finally,reference pixels for boundary filtering are selected according to theprediction mode of the current intra prediction block, and filtercoefficients are selected according to the size of the prediction block,and the current prediction value is filtered using the reference pixelsto obtain a new intra prediction value; wherein the value of N isdetermined by the characteristics of different intra prediction modesand intra prediction blocks of different sizes.
 2. The method accordingto claim 1, characterized in that the flag of the bitstream to identifywhether intra prediction block boundary filtering is used for intraprediction is 1-bit.
 3. The method according to claim 1, characterizedin that the filtering is performed on the first 10 rows or the first 10columns of the intra prediction block at most.
 4. A boundary filteringmethod for intra prediction, whether boundary filtering is performed onan intra prediction block or not is adaptively selected by means of arate distortion optimization decision; during filtering, a filtercoefficient exponentially attenuated relative to distance to boundary isadopted to perform filtering on the first N rows or the first N columnsof the intra prediction block by means of an intra prediction blockfilter, and different filtering strengths are used according todifferent sizes of the prediction blocks, comprising: 1) at the encodingside, performing rate-distortion optimization on each coding unit;comprising: 11) performing intra prediction block filtering for eachcoding unit; 12) determining whether intra prediction block boundaryfiltering should be used at the encoding side by means of a ratedistortion optimization decision; transmitting a flag to the bitstreamto identify whether intra prediction block boundary filtering is usedfor intra prediction; 13) when intra prediction block boundary filteringshould be used at the encoding side, intra boundary filtering coding isperformed by the intra prediction block filter, which including thefollowing processes: first, obtaining reference pixels adjacent to thecurrent block from the reconstructed prediction blocks; subsequently,intra prediction is performed according to the prediction direction ofthe intra prediction block to obtain an intra prediction value; finally,reference pixels for boundary filtering are selected according to theprediction mode of the current intra prediction block, and filtercoefficients are selected according to the size of the prediction block;the current prediction value is subjected to boundary filtering usingthe reference pixels to obtain a new intra prediction value; 2) at thedecoding side, reading the flag in the bitstream for each coding unitand decoding according to the flag, which including the followingprocesses: 21) determining whether intra prediction block boundaryfiltering should be used at the decoding side; 22) when intra predictionblock boundary should be used at the decoding side, intra boundaryfiltering decoding is performed by the intra prediction block filter,which including the following processes: first, obtaining referencepixels adjacent to the current block from the reconstructed predictionblocks; then, intra prediction is performed to obtain the intraprediction value according to the prediction mode of the intraprediction block that is obtained by decoding; finally, reference pixelsfor boundary filtering are selected according to the prediction mode ofthe current intra prediction block, and filter coefficients are selectedaccording to the size of the prediction block, and the currentprediction value is filtered using the reference pixels to obtain a newintra prediction value; wherein the value of N is determined by thecharacteristics of different intra prediction modes and intra predictionblocks of different sizes; wherein the intra prediction block filter isa three-tap filter, which is expression as formula 1:P′(x,y)=w _(left)(x)·P(−1,y)+w _(top)(y)·P(x,−1)+(1−w _(left)(x)−w_(top)(y))·P(x,y)0≤x,y<N  (formula 1) for a prediction pixel, two reference pixels, pixelP(−1,y) in the same row thereof and pixel P(x,−1) in the same columnthereof, are used for filtering, wherein, w_(left)(x) and w_(top)(y) arethe boundary filtering coefficients of the two reference pixelsrespectively, P(x,y) is the predicted pixel after the intra prediction;P′(x,y) is the pixel after the intra prediction block filtering; x, yare the coordinates within the prediction block, it is the first columnin the prediction block when x=0, it is the first row in the predictionblock when y=0; n is the number of rows or columns.
 5. The methodaccording to claim 4, characterized in that for the intra predictionblock filter, when w_(top)(y) attenuates to 0, the intra predictionblock filter degenerates into a two-tap filter, as shown in formula 2:P′(x,y)=w _(left)(x)·P(−1,y)+(1−w _(left)(x))·P(x,y),x<N   (formula 2)P′(x,y)=w _(top)(y)·P(x,−1)+(1−w _(top)(y))·P(x,y),y<N   (formula 3)when w_(left)(y) attenuates to 0, the intra prediction block filterdegenerates into a two-tap filter, as shown in formula
 3. 6. A boundaryfiltering method for intra prediction, whether boundary filtering isperformed on an intra prediction block or not is adaptively selected bymeans of a rate distortion optimization decision; during filtering, afilter coefficient exponentially attenuated relative to distance toboundary is adopted to perform filtering on the first N rows or thefirst N columns of the intra prediction block by means of an intraprediction block filter, and different filtering strengths are usedaccording to different sizes of the prediction blocks, comprising: 1) atthe encoding side, performing rate-distortion optimization on eachcoding unit; comprising: 11) performing intra prediction block filteringfor each coding unit; 12) determining whether intra prediction blockboundary filtering should be used at the encoding side by means of arate distortion optimization decision; transmitting a flag to thebitstream to identify whether intra prediction block boundary filteringis used for intra prediction; 13) when intra prediction block boundaryfiltering should be used at the encoding side, intra boundary filteringcoding is performed by the intra prediction block filter, whichincluding the following processes: first, obtaining reference pixelsadjacent to the current block from the reconstructed prediction blocks;subsequently, intra prediction is performed according to the predictiondirection of the intra prediction block to obtain an intra predictionvalue; finally, reference pixels for boundary filtering are selectedaccording to the prediction mode of the current intra prediction block,and filter coefficients are selected according to the size of theprediction block; the current prediction value is subjected to boundaryfiltering using the reference pixels to obtain a new intra predictionvalue; 2) at the decoding side, reading the flag in the bitstream foreach coding unit and decoding according to the flag, which including thefollowing processes: 21) determining whether intra prediction blockboundary filtering should be used at the decoding side; 22) when intraprediction block boundary should be used at the decoding side, intraboundary filtering decoding is performed by the intra prediction blockfilter, which including the following processes: first, obtainingreference pixels adjacent to the current block from the reconstructedprediction blocks; then, intra prediction is performed to obtain theintra prediction value according to the prediction mode of the intraprediction block that is obtained by decoding; finally, reference pixelsfor boundary filtering are selected according to the prediction mode ofthe current intra prediction block, and filter coefficients are selectedaccording to the size of the prediction block, and the currentprediction value is filtered using the reference pixels to obtain a newintra prediction value; wherein the filter coefficient exponentiallyattenuated relative to distance to boundary is used for filtering,wherein the filter coefficients are expressed in formula 4 and formula 5respectively: $\begin{matrix}{w_{top} = \frac{n_{top}}{2^{y}}} & \left( {{formula}\mspace{14mu} 4} \right) \\{w_{left} = \frac{n_{left}}{2^{x}}} & \left( {{formula}\mspace{14mu} 5} \right)\end{matrix}$ where, n_(top) and n_(left) are filter coefficients usedfor filtering with the first row and the first column of the predictionblock, respectively.
 7. A boundary filtering method for intraprediction, whether boundary filtering is performed on an intraprediction block or not is adaptively selected by means of a ratedistortion optimization decision; during filtering, a filter coefficientexponentially attenuated relative to distance to boundary is adopted toperform filtering on the first N rows or the first N columns of theintra prediction block by means of an intra prediction block filter, anddifferent filtering strengths are used according to different sizes ofthe prediction blocks, comprising: 1) at the encoding side, performingrate-distortion optimization on each coding unit; comprising: 11)performing intra prediction block filtering for each coding unit; 12)determining whether intra prediction block boundary filtering should beused at the encoding side by means of a rate distortion optimizationdecision; transmitting a flag to the bitstream to identify whether intraprediction block boundary filtering is used for intra prediction; 13)when intra prediction block boundary filtering should be used at theencoding side, intra boundary filtering coding is performed by the intraprediction block filter, which including the following processes: first,obtaining reference pixels adjacent to the current block from thereconstructed prediction blocks; subsequently, intra prediction isperformed according to the prediction direction of the intra predictionblock to obtain an intra prediction value; finally, reference pixels forboundary filtering are selected according to the prediction mode of thecurrent intra prediction block, and filter coefficients are selectedaccording to the size of the prediction block; the current predictionvalue is subjected to boundary filtering using the reference pixels toobtain a new intra prediction value; 2) at the decoding side, readingthe flag in the bitstream for each coding unit and decoding according tothe flag, which including the following processes: 21) determiningwhether intra prediction block boundary filtering should be used at thedecoding side; 22) when intra prediction block boundary should be usedat the decoding side, intra boundary filtering decoding is performed bythe intra prediction block filter, which including the followingprocesses: first, obtaining reference pixels adjacent to the currentblock from the reconstructed prediction blocks; then, intra predictionis performed to obtain the intra prediction value according to theprediction mode of the intra prediction block that is obtained bydecoding; finally, reference pixels for boundary filtering are selectedaccording to the prediction mode of the current intra prediction block,and filter coefficients are selected according to the size of theprediction block, and the current prediction value is filtered using thereference pixels to obtain a new intra prediction value; wherein thefilter coefficients of floating point are converted to integers by usingthe filtering method shown in formula 6, 7 and 8, and the right shiftoperation is carried out after filtering to avoid floating pointcalculation:P′(x,y)=(w _(left)(x)·P(−1,y)+w _(top)(y)·P(x,−1)+(64−w _(left)(x)−w_(top)(y)·P(x,y)+32)>>6   (formula 6)P′(x,y)=(w _(left)(x)·P(−1,y)+(64−w _(left)(x))·P(x,y)+32)>>6   (formula7)P′(x,y)=(w _(top)(y)·P(x,−1)+(64−w _(top)(y))·P(x,y)+32)>>6   (formula8).
 8. A boundary filtering method for intra prediction, whetherboundary filtering is performed on an intra prediction block or not isadaptively selected by means of a rate distortion optimization decision;during filtering, a filter coefficient exponentially attenuated relativeto distance to boundary is adopted to perform filtering on the first Nrows or the first N columns of the intra prediction block by means of anintra prediction block filter, and different filtering strengths areused according to different sizes of the prediction blocks,comprising: 1) at the encoding side, performing rate-distortionoptimization on each coding unit; comprising: 11) performing intraprediction block filtering for each coding unit; 12) determining whetherintra prediction block boundary filtering should be used at the encodingside by means of a rate distortion optimization decision; transmitting aflag to the bitstream to identify whether intra prediction blockboundary filtering is used for intra prediction; 13) when intraprediction block boundary filtering should be used at the encoding side,intra boundary filtering coding is performed by the intra predictionblock filter, which including the following processes: first, obtainingreference pixels adjacent to the current block from the reconstructedprediction blocks; subsequently, intra prediction is performed accordingto the prediction direction of the intra prediction block to obtain anintra prediction value; finally, reference pixels for boundary filteringare selected according to the prediction mode of the current intraprediction block, and filter coefficients are selected according to thesize of the prediction block; the current prediction value is subjectedto boundary filtering using the reference pixels to obtain a new intraprediction value; 2) at the decoding side, reading the flag in thebitstream for each coding unit and decoding according to the flag, whichincluding the following processes: 21) determining whether intraprediction block boundary filtering should be used at the decoding side;22) when intra prediction block boundary should be used at the decodingside, intra boundary filtering decoding is performed by the intraprediction block filter, which including the following processes: first,obtaining reference pixels adjacent to the current block from thereconstructed prediction blocks; then, intra prediction is performed toobtain the intra prediction value according to the prediction mode ofthe intra prediction block that is obtained by decoding; finally,reference pixels for boundary filtering are selected according to theprediction mode of the current intra prediction block, and filtercoefficients are selected according to the size of the prediction block,and the current prediction value is filtered using the reference pixelsto obtain a new intra prediction value; wherein different filteringstrengths are used according to different sizes of the intra predictionblocks, wherein filter intensity parameters n_(top) and n_(left) areobtained according to a prediction distortion training of the intraprediction block.
 9. The method according to claim 8, characterized inthat according to the prediction distortion distribution based on thestatistics of 16×16 intra prediction block in HEVC, the filteringintensity parameters n_(top) and n_(left) are defined to be proportionalto the magnitude of prediction distortion, which are expressed asformula 9 and 10: $\begin{matrix}{n_{top} = {\min\left( {\frac{d_{top}}{16},1} \right)}} & \left( {{formula}\mspace{14mu} 9} \right) \\{n_{left} = {\min\left( {\frac{d_{left}}{16},1} \right)}} & \left( {{formula}\mspace{14mu} 10} \right)\end{matrix}$ wherein, d_(top) is the average prediction distortionvalue of the first row at the top of the prediction block, and d_(left)is the average prediction distortion value of the first column on theleft of the prediction block, “min” means take the minimum value of twovalues.